Weeks Calculator – Add or Subtract Weeks from Any Date

What this tool does. The Weeks Calculator is your flexible version of “weeks from today” style tools. Instead of being locked to the current date, you can choose any start date, type how many weeks you want to move, and instantly see the exact resulting date. To go forward in time, enter a positive number. To go back in time, just add a minus sign (for example, -6 weeks). Everything lives in one clean white card: a clear start date row, one simple weeks field, and a bold result you can trust.

How it works. First, you select the start date using the month, day, and year dropdowns. The calculator validates that the date is real (including correct handling of leap years and month lengths). Next, you enter how many whole weeks you’d like to move. Under the hood, the tool converts your weeks into days (weeks × 7), shifts the chosen date forward or backward depending on the sign of your input, and prints the exact target date in a human-readable format. There’s no extra direction selector to worry about: positive = after, negative = before, and 0 = same date.

Why weeks-based math matters. We plan in weeks constantly: agile sprints, school units, newsletter cadences, content drops, coaching programs, workout cycles, billing periods, and more. But “8 weeks from this milestone” or “12 weeks before that deadline” is where hand-counting goes wrong, especially when crossing months, holidays, and year boundaries. The Weeks Calculator exists to kill that friction. You set the anchor date (a launch, exam, event, or cutoff), move by a clean number of weeks (with + or −), and get an answer you can paste straight into docs, timelines, or ticket systems.

Add and subtract with one field. Need to know when a 10-week course ends if it starts on a specific Monday? Choose the start Monday, type 10, hit Calculate date, and you’re done. Want to find the date 6 weeks before a key event? Select the event date as your start date, type -6, and run it again. The result card updates instantly, and the breakdown line confirms your start date, sign, weeks, total days, and final target date so you can sanity-check at a glance without fiddling with multiple controls.

Straight-line breakdown. The result is designed as a single, screenshot-friendly line of truth. You’ll see a title like Date 8 weeks after January 1, 2026: followed by the full long-form date. Below that, the facts row lays out: the exact start date, whether your input moved you forward or backward, how many weeks that represents (including the sign), the equivalent number of days, and the final target date. Everything is inline, no scattered tables or hidden math.

Practical use cases. Use the Weeks Calculator to line up sprints against releases, check if a campaign window matches a multi-week brief, plan phased rollouts, back-calculate when to start prep work, or schedule recurring reviews. It’s ideal for academic terms, HR probationary periods, maintenance cycles, and anything defined as “X weeks before/after” another event. If you already like the Weeks From Today Calculator and Days From Today Calculator, this page gives you the same feel but with the freedom to anchor your own custom start date.

Step-by-step. Pick a Start date using the dropdowns. Enter a whole number of weeks in the field — examples include 0, 1, 4, 8, 12, 26, 52, or negative values like -2, -6, -10 if you want to move backwards. Click Calculate date or press Enter while focused in the weeks box. The answer appears immediately in the result card. Change the number as needed; there’s no reset button cluttering the layout, and you don’t have to flip any separate “add/subtract” toggle.

When you need other views. If you only care about moving forward from today, use the dedicated Weeks From Today Calculator. To see the number of weeks between two fixed dates, jump to the Weeks Between Dates Calculator. And if your scenario is naturally days-based instead of weeks-based, the Days From Today Calculator is tuned for that. All of these tools share the same clean layout and local, in-browser calculations.

Accuracy & privacy. All calculations run locally in your browser using real calendar rules. Leap years, month lengths, and year boundaries are respected automatically. Your chosen dates and inputs are never sent to a server, logged, or stored — which makes this safe for internal deadlines, legal-sensitive schedules, or client-facing timelines. As long as your device’s date and time zone are correct, the Weeks Calculator will match what your calendar app shows.